Video: NASA: Debris won't stop shuttle landing

HOUSTON — Friday’s brief orbital anxiety about threats from an unidentified object seen out the window of space shuttle Discovery underscore why NASA has always been interested in what can justifiably be called UFOs.

The incident explains a lot about the procedures and practices for dealing with unusual naked eye or camera sightings of the "stuff" outside spaceship windows.

It has nothing to do with widely circulated stories of alien visitors, clandestine radio channels or supposedly top-secret "standing orders" to avoid discussions of such sightings — or even lie about them. As was evident Friday morning, just the opposite is true: Strange stuff gets reported as soon as it is spotted on open channels.

The reason is life-and-death. Since Mercury days, NASA engineers have realized that visual sightings of anomalies can sometimes provide clues to the functioning — or malfunctioning — of the spaceships that contain their precious astronauts. White dots outside the window could be spray from a propellant leak, or ice particles, flaking insulation, worked-loose fasteners (as in this latest case) or inadvertently released tools or components.

Whatever the objects might be, they pose a threat of coming back in contactwith the spacecraft, potentially causing damage to delicate instruments, thermal tiles, windows or solar cells, or fouling rotating or hinged mechanisms. So Mission Control needs to find out about them right away in order to determine that they are not hazardous.

The overlooked clue
Most spacecraft dandruff never gets seen. It can drift away at night, or come from an area of the spacecraft that's not under observation, or just get overlooked. And in almost every case, it hasn’t mattered.

But once in a great while, failure to observe something outside can be fatal. The saddest missed opportunity in space history came in January 2003, when Columbia was damaged during launch by a falling piece of insulation. The impact put a head-sized break in the left wing's leading edge, but the damage was not visible to sensors.

Then, on the second day of the flight, the plate-sized fragment of the heat shield worked loose after some routine thruster firings and drifted away. Which windows it passed, and which external TV cameras, can never be determined. Its departure wasn’t even realized until post-disaster analysis of raw radar tracking reports showed a small "blip" in the noise of the radar echoes.

Second-guessing is uncertain, but space experts find it plausible that a sighting of the departing fragment, and perhaps even photographs of it while it was still only a few hundred feet away, might have nudged NASA officials into taking a closer look at the already-suspect thermal protection system in that area. If that closer look had led to the discovery of the spaceship’s lethal wound, then NASA would have mobilized both emergency repair and rescue efforts. Nobody can say whether they might have saved the lives of the crew, but at least they would have gone down swinging, forewarned and trying their best.

Chasing down the fireflies
These kinds of "bogies" have occurred on astronaut missions since John Glenn’s flight in February 1962. His flock of "fireflies" was visually stunning and not a little worrisome, until it became clear it was caused by ice flakes from an exterior-mounted coolant mechanism that sucked heat out of the spacecraft by spraying water against a radiator.

Fellow Mercury astronaut Wally Schirra noted that some of the fireflies were droplets of urine expelled from the spacecraft's life support system. "We peed all over the world," he said.

During Gemini missions, the crews often opened their hatch to throw out used-up equipment and trash, and sometimes saw the objects
looping back toward them
a few hours later. The jettisoned booster upper stage could sometimes be seen, especially on later missions where the astronauts changed their orbits. On lunar missions, the jettisoned last rocket stage and a set of garage-door-sized support panels often coasted out to the moon within visual range (a few hundred miles) of the Apollo spacecraft, and several crews mentioned seeing them too.

Some ‘moon pigeons’ unexplained
After mysterious dots were filmed passing by the windows during Apollo 12, NASA commissioned a special study on how to extract useful engineering data from such sightings. Published in 1970, the report referred to such apparitions as “moon pigeons."

The study associated the images with known spacecraft events such as explosive bolt initiation and water (or urine) dumps, but the authors conceded that all observations could not be unambiguously solved.

“In general, it takes much more information to identify an object than it does to detect it,” they said. Nevertheless, they concluded, “these data will undoubtably be of use to the engineering, scientific and public relations communities.”

During space shuttle missions, most of the apparitions involved frozen water or propellant, leaking from thrusters or just flaking off the cryogenic fuel lines at the back end of the space plane. Strips of insulation and retention straps sometimes wiggle their way past the windows. Thruster firings during maneuvers often shake stuff loose. The unusual sightings involved other satellites, or features on Earth’s nightside — or on a few occasions, that old standby of UFO misperceptions, Venus.

If such sightings have any safety value, it is only when they are promptly and fully reported. That happened perfectly on this shuttle mission, and it allowed Mission Control to identify the "UFO" quickly and confidently determine that it posed no hazard. So the old saw applies, to “watch the skies” — even if you are up there in the skies yourself.

NBC News space analyst James Oberg spent 22 years at NASA's Johnson Space Center as a Mission Control operator and an orbital designer.

The 12 orbiting astronauts on the International Space Station were hailed by the chief on Thursday — and also got a humorous scolding for keeping their android crewmate locked up in its packing for so long.